Btrfs: reduce lock contention during extent insertion (dc7fdde3) · Commits · 戴 / test

We're spending huge amounts of time on lock contention during end_io processing because we unconditionally assume we are overwriting an existing extent in the file for each IO. This checks to see if we are outside i_size, and if so, it uses a less expensive readonly search of the btree to look for existing extents. Signed-off-by:

Chris Mason <chris.mason@oracle.com>

fs/btrfs/file.c

+7 −2

Original line number	Diff line number	Diff line
		@@ -567,6 +567,7 @@ int btrfs_drop_extents(struct btrfs_trans_handle trans, struct inode inode,
		int extent_type;
		int recow;
		int ret;
		int modify_tree = -1;

		if (drop_cache)
		btrfs_drop_extent_cache(inode, start, end - 1, 0);
		@@ -575,10 +576,13 @@ int btrfs_drop_extents(struct btrfs_trans_handle trans, struct inode inode,
		if (!path)
		return -ENOMEM;

		if (start >= BTRFS_I(inode)->disk_i_size)
		modify_tree = 0;

		while (1) {
		recow = 0;
		ret = btrfs_lookup_file_extent(trans, root, path, ino,
		search_start, -1);
		search_start, modify_tree);
		if (ret < 0)
		break;
		if (ret > 0 && path->slots[0] > 0 && search_start == start) {
		@@ -634,7 +638,8 @@ next_slot:
		}

		search_start = max(key.offset, start);
		if (recow) {
		if (recow \|\| !modify_tree) {
		modify_tree = -1;
		btrfs_release_path(path);
		continue;
		}

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